<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" type="text/css" href="../css/class选择器.css"/>
</head>
<body>
/*class选择器，值不能以数字开头*/
<div class="c123">独占一行</div><br/>
<div class="c222">独占一行</div><br/>
<div class="c123">独占一行</div><br/>

<span class="c222">根据数据长度进行封装</span>
<span class="c223">根据数据长度进行封装</span>
<span class="c224">根据数据长度进行封装</span>

</body>
</html>